A technique of measuring electromagnetic wave generated by scattering is dependent upon a technique of measuring electromagnetic wave by installing an isolation antenna capable of isolating a transmitting signal and a receiving signal in an outdoor test station having a radio wave absorbent on its bottom, or a radio dark room having a radio wave absorbent on its ceiling, sidewall and bottom.
On the other hand, an inverse scattering measurement must satisfy a far field condition, and thus, an antenna and a test object must be spaced far from each other.
Therefore, a large radio dark room is necessary, and electromagnetic wave is generated and received through the antenna, thereby restricting a bandwidth, which is a general problem of the antenna. In addition, a phase linear response to a frequency is not guaranteed in a broadband. Especially, the size of the antenna is very large in a low frequency band, which is very difficult to measure inverse scattering in a low frequency.
Furthermore, in case of implementing an isolation antenna for measuring inverse scattering, a transmitting antenna and a receiving antenna must be installed adjacently to each other. Moreover, interference wave scattered from accidental scattering objects (such as receiving antenna, transmitting/receiving antenna cable, signal generator, receiver, etc.) except its adjacent test object may be mixed with an original signal, thereby making it difficult to embody the measurement system.
To solve the above problem, a technique of removing an interference wave signal is applied to a receiver in which the receiving antenna is installed. However, this technique requires very high-priced facilities and circuit system, and is very sensitive to environmental variations of the radio dark room. Therefore, if there is a change in the surrounding environment, it is difficult to ensure that the signal has been scattered directly from the test object. In addition, reproducibility and accuracy in measurement are low. Also, since the radio wave absorbent must be installed on all of the bottom, sidewall and ceiling of the radio dark room, the installation space is inevitably enlarged to satisfy the far field condition, which increases expenses.
Besides, the outdoor test station is also affected by the external electromagnetic wave environment.
As a result, the above-mentioned prior art does not embody the method for measuring the inverse scattering wave, which can measure performance of an RFID transponder or reader in a narrow space such as a production line, regardless of the external electromagnetic wave environment.